/*
 * Copyright 2018 The Cartographer Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef CARTOGRAPHER_COMMON_TASK_H_
#define CARTOGRAPHER_COMMON_TASK_H_

#include <set>

#include "absl/synchronization/mutex.h"
#include "glog/logging.h"
#include "thread_pool.h"

namespace cartographer
{
    namespace common
    {
        class ThreadPoolInterface;

        class Task
        {
        public:
            friend class ThreadPoolInterface;

            using WorkItem = std::function<void()>;
            // 新增，已分派，依赖已完成，正在运行，已完成
            enum State
            {
                NEW,
                DISPATCHED,
                DEPENDENCIES_COMPLETED,
                RUNNING,
                COMPLETED
            };

            Task() = default;
            ~Task();

             // 得到该 任务 的状态
            State GetState() LOCKS_EXCLUDED(mutex_);

            // State must be 'NEW'.
            void SetWorkItem(const WorkItem &work_item) LOCKS_EXCLUDED(mutex_);

            // State must be 'NEW'. 'dependency' may be nullptr, in which case it is assumed completed.
            //依赖可以为空，但任务必须是 new
            void AddDependency(std::weak_ptr<Task> dependency) LOCKS_EXCLUDED(mutex_);

        private:
            // Allowed in all states.
            void AddDependentTask(Task *dependent_task);

            // State must be 'DEPENDENCIES_COMPLETED' and becomes 'COMPLETED'.
            void Execute() LOCKS_EXCLUDED(mutex_);

            // State must be 'NEW' and becomes 'DISPATCHED' or 'DEPENDENCIES_COMPLETED'.
            void SetThreadPool(ThreadPoolInterface *thread_pool) LOCKS_EXCLUDED(mutex_);

            // State must be 'NEW' or 'DISPATCHED'. If 'DISPATCHED', may become
            // 'DEPENDENCIES_COMPLETED'.
            void OnDependenyCompleted();

            WorkItem work_item_ GUARDED_BY(mutex_);
            ThreadPoolInterface *thread_pool_to_notify_ GUARDED_BY(mutex_) = nullptr;
            State state_ GUARDED_BY(mutex_) = NEW;
            unsigned int uncompleted_dependencies_ GUARDED_BY(mutex_) = 0;
            std::set<Task *> dependent_tasks_ GUARDED_BY(mutex_);

            absl::Mutex mutex_;
        };

    } // namespace common
} // namespace cartographer

#endif // CARTOGRAPHER_COMMON_TASK_H_
